Enhancing the width of polycrystalline grains with mask

ABSTRACT

A system, method and masking arrangement are provided of enhancing the width of polycrystalline grains produced using sequential lateral solidification using a modified mask pattern is disclosed. One exemplary mask pattern employs rows of diamond or circular shaped areas in order to control the width of the grain perpendicular to the direction of primary crystallization.

FIELD OF THE INVENTION

The present invention relates to semiconductor processing techniques,and more particularly, techniques for fabricating semiconductorssuitable for use as thin-film transistor (“TFT”) devices.

BACKGROUND INFORMATION

During the past several years, sequential lateral solidification (“SLS”)techniques have been developed to generate quality large grainedpolycrystalline thin films, e.g., silicon films, having a substantiallyuniform grain structure. For example, in U.S. Pat. No. 6,322,625, issuedto Im and U.S. patent application Ser. No. 09/390,537 (the “'537application”), the entire disclosures of which are incorporated hereinby reference, particularly advantageous apparatus and methods forgrowing large grained polycrystalline or single crystal siliconstructures using energy-controllable laser pulses and small-scaletranslation of a silicon sample to implement sequential lateralsolidification have been described. As described in these patentdocuments, at least portions of the semiconductor film on a substrateare irradiated with a suitable radiation pulse to completely melt suchportions of the film throughout their thickness.

In order to increase throughput, continuous motion SLS processes havebeen proposed. Referring to FIG. 1, such system preferably includes anexcimer laser 110, an energy density modulator 120 to rapidly change theenergy density of a laser beam 111, a beam attenuator and shutter 130,optics 140, 141, 142 and 143, a beam homogenizer 144, a lens and beamsteering system 145, 148, a masking system 150, another lens and beamsteering system 161, 162, 163, an incident laser pulse 164, a thin filmsample on a substrate 170 (e.g., a silicon thin film) a sampletranslation stage 180, a granite block 190, a support system 191, 192,193, 194, 195, 196, and a computer 100 which manages X and Y directiontranslations and microtranslations of the film sample and substrate 170.The computer 100 directs such translations and/or microtranslations byeither a movement of a mask within masking system 150 or by a movementof the sample translation stage 180. As described in U.S. Pat. No.6,555,449 issued to Im, the entire disclosure of which is incorporatedherein by reference, the sample 170 may be translated with respect tothe laser beam 149, either by moving the masking system 150 or thesample translation stage 180, in order to grow crystal regions in thesample 170.

FIG. 2 depicts the mask used in the continuous motion SLS process asdescribed in International Publication No. 02/086954 (the “'954Publication”), the entire disclosure of which is incorporated herein byreference. This mask is divided into a first mask section 20 and asecond mask section 22. The first mask section 20 can be used for thefirst pass under the laser. The second mask section 22 is used on thesecond pass. The first mask section 20 may have corresponding opaqueareas 24 and clear areas 25. Throughout the specification of the '954Publication and the present application, “opaque areas” are referred toas areas of the mask that prevent associated regions of a thin filmsample irradiated by beams passed through the mask from being completelymelted throughout its thickness, while “clear areas” are areas of themask that permit associated regions of a thin film sample irradiated bybeams passed through the mask to be completely melted throughout itsthickness. The clear areas can be actual holes in the mask or may besections of the mask that allow the sample behind it to be completelymelted throughout its thickness. The second mask section 22 also hascorresponding opaque areas 26 and clear areas 27. The opaque areas 24,26 of both sections 20, 22 are areas that prevent radiation from a lasersource from passing through to the sample. The shape of these clearareas, both in the second mask section 22 and in the first mask section20, generally have a shape of “straight slits.” The array of the clearareas 24 in the first mask section 20 are generally staggered from thearray of clear areas 26 in the second mask section 22. As indicatedabove, the clear areas 25, 27 of both sections allows radiation to passthrough to melt the sample below the surface of the mask.

FIG. 3 depicts the radiation pattern passing through the mask of FIG. 2during processing of the film. The first pattern section 30 shows thepattern that results after the first pass of the irradiation by thepulses shaped using the mask. The pulse passing through the mask mayhave a first portion 34 that corresponds to the pattern of the firstmask section 20. The clear areas of the first mask section 20 in FIG. 2allow the radiation to pass therethrough, and melt the thin filmthroughout its thickness, thus resulting in a first melted region and anunmelted region 44 (see FIG. 4) after the first pass of the sampleprocessing. When the mask is translated in the direction of the arrow33, the second pattern section 32 of FIG. 3 with the radiation patternresults after the second pass of processing the sample. The pulsepassing through the mask may have a second portion 36 that correspondsto the pattern of the second mask section 22. The clear areas of thesecond mask section 22 of the mask in FIG. 2 allow the radiation to passtherethrough, and again melt the thin film throughout its thickness.This results in a second melted region and an unmelted region over thegrain boundary 45 (see FIG. 4).

FIG. 4 depicts the resulting crystalline structure that is producedusing the mask of FIG. 2. The first structure section 40 includes thestructure 41 that results after the first pass of the sample processing.The opaque areas of the first mask section 20 of the mask of FIG. 2prevent the associated regions 44 from completely melting. A grainboundary 45 in the direction of the crystalline structure formsapproximately halfway between the associated regions 44. The secondstructure section 42 includes the crystalline structure 48 that resultsafter the second pass of the sample processing. The grain boundary 45from the first pass is not removed, while the individual grains expandin length until they meet one another, because all areas are exposed tothe laser during the second pass except the area that corresponds to thegrain boundary 45. Thus, the grain length 46 (parallel to the directionof the crystalline structure) may be controlled by the properties andslit patterns of the mask of FIG. 2. The width 47 of the grain(perpendicular to the direction of the crystalline structure), however,is not very easily controlled. Indeed, it may be primarily dependent onthe characteristics of the film.

As noted above, the aforementioned SLS techniques typically employ astraight slit mask pattern. This allows for the ease of control of thegrain length (in the direction of the primary crystallization). In suchcase, the perpendicular grain spacing may be dependent on the propertiesof the film, and thus is not very easily manipulated. While thetailoring of the shaped areas to manipulate the microstructure has beenemployed in other SLS methods and systems, such as with the use ofchevron-shaped openings in a mask, the techniques associated therewithmay produce narrow grain areas. Accordingly, there is a need to controlgrain length in the thin film, as well as increase the area in which asmaller number of grains are present.

SUMMARY OF THE INVENTION

The present invention overcomes the above-mentioned problems byproviding a mask having a row of point-type areas (e.g., diamond and/ordot patterned opaque regions) provided thereon. Such mask pattern thatuses closely spaced circular or diamond-shaped areas is utilized in lieuof the straight slits in at least a portion of the mask in order toproduce a microstructure with wider grain areas. Using the mask of thisconfiguration according to the present invention advantageously affectsa melt interface curvature on the evolution of grain boundaries tofavorably increase the perpendicular grain boundary spacing.

According to one exemplary embodiment of the present invention, amasking arrangement, system and process are provided for processing athin film sample, e.g., an amorphous silicon thin film, into apolycrystalline thin film. In particular, a mask can be utilized whichincludes a first section having at least one opaque areas arranged in afirst pattern, e.g., diamond areas, oval areas, and/or round areas. Thefirst section may be configured to receive a beam pulse thereon, andproduce a first modified pulse when the beam pulse is passedtherethrough. The first modified pulse may include at least one firstportion having a pattern that corresponds to the first pattern of thefirst section. When the first portion is irradiated on the sample, atleast one first region of the sample is prevented from being completelymelted throughout its thickness. The mask may also includes a secondsection associated with the first section, with the second sectionincluding a further area arranged in a second pattern. The secondsection may be configured to receive a further beam pulse thereon, andproduce a second modified pulse when the further beam pulse is passedtherethrough. The second modified pulse can include at least one secondportion having a pattern that corresponds to the second pattern of thesecond section. When the second portion is irradiated on the sample, atleast one second region of the sample irradiated by the second portionis completely melted throughout its thickness. In addition, when thefirst region is irradiated by the second modified pulse, the secondportion of the second modified pulse completely melts the first regionthroughout its thickness.

The accompanying drawings, which are incorporated and constitute part ofthis disclosure, illustrate preferred embodiments of the invention andserve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional diagram of a conventional system for performingsemiconductor processing including sequential lateral solidification ofa thin film;

FIG. 2 is a top view of a conventional mask;

FIG. 3 is a schematic top view showing the radiation pattern associatedwith the mask of FIG. 2;

FIG. 4 is a schematic top view showing grain spacing in the processedthin film that results from use of the mask of FIG. 2;

FIG. 5 is a top view of a mask according to an exemplary embodimentaccording to the present invention;

FIG. 6 is a top view of an irradiation pattern generated by the mask ofFIG. 5;

FIG. 7 is a top view of a grain spacing produced by the mask of FIG. 5;and

FIG. 8 is a top view of a mask according to an exemplary embodimentaccording to the present invention;

FIG. 9 is a top view of a grain spacing produced by the mask of FIG. 8;and

FIG. 10 is a flow diagram illustrating the steps according to thepresent invention implemented by the system of FIG. 1.

Throughout the FIGS., the same reference numerals and characters, unlessotherwise stated, are used to denote like features, elements, componentsor portions of the illustrated embodiments. Moreover, while the presentinvention will now be described in detail with reference to the FIGS.,it is done so in connection with the illustrative embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 5-7, a presently preferred embodiment of the presentinvention will be described. This embodiment utilizes an exemplary maskpattern according to the present invention which uses preferably closelyspaced circular or diamond-shaped areas in order to produce amicrostructure with wider areas of limited number of grains providedtherein. Those skilled in the art should understand that the systems,methods, and masks according to the present invention are applicable notonly to single-shot motion SLS processes and systems, but also to thinfilms that have been processed with n-shot and 2n-shot SLS techniques.

Referring to FIG. 5, the mask which may be used in an exemplaryembodiment of the present invention may be divided into a first masksection 50 and a second mask section 52. Alternatively, two separatemasks may be used instead of separate sections in one mask. The firstmask section 50 may be used to process a selected area of the thin filmas an initial shot. The second mask section 52 may be used as a secondshot which immediately follows the first shot. The first mask section 50may have corresponding opaque areas 54 and clear areas 55. The secondmask section 52 may also have corresponding opaque areas 56 and clearareas 57. While the shape of these opaque areas in the second masksection 52 may be in the shape of traditional “straight slits” asdescribed herein above in FIGS. 2-4, the opaque areas in the first masksection 50 are preferably provided in rows of diamonds, circular shaped,and/or oval shaped areas. The array of opaque areas 54 in the first masksection may be staggered from the array of opaque areas 56 in the secondmask section.

FIG. 6 depicts the radiation pattern that may be shaped by the mask ofFIG. 5 upon passing a beam pulse therethrough. In particular, the firstpattern section 60 includes the pattern that may result upon the firstshaped pulse impacting the corresponding portions on the sample. A pulseshaped by the mask may have a first portion 64 that corresponds to thepattern of the first mask section 50. The opaque mask areas 54 of thefirst mask section 50 in FIG. 5 may block the radiation from passingthrough to the thin film sample, and thus result in a first unmeltedregion 74 in the first pass (see FIG. 7). As shown in FIG. 7, the grainsgrow outwardly from the unirradiated areas because they seed the meltedregions upon the resolidification of the melted areas. Thus, the widthof the resolidified regions is based on the grain growth into twoopposite directions. This is because the grains grow outward from theunmelted regions, e.g., in the opposite directions thereof. Parallelgrain boundaries 75, as shown in FIG. 7, are foamed when the graingrowth from neighboring regions produced by the pattern of the firstmask section 50 impact one another. In this manner, approximatelyhorizontal borders between resolidified regions may be formed. When themask is shifted in the direction of the arrow 63, the beam is translatedand/or the sample may be translated in the opposite direction of thearrow 63 by the translation stage, the second pattern section 62 of FIG.6 shows the radiation pattern that may result after the second shotirradiates the corresponding portions of the thin film. In particular, apulse passing through the mask may have a second portion 66 thatcorresponds to the pattern of the second mask section 52. The opaqueareas 56 of the second mask section 52 of the mask in FIG. 5 may preventthe sample irradiated by pulses that are shaped by the mask from beingcompletely melted throughout its thickness. This may result in ageneration of second melted region, and an unmelted region which isprovided over the unmelted grain boundary 75 (see FIG. 7).

FIG. 7 depicts the resulting crystalline structure that may developusing the mask of FIG. 5. The first structure section 70 includes astructure 71 that may be produced after irradiation thereof by the firstbeam pulse. The opaque areas of the first section of the mask of FIG. 5prevent the associated regions 74 from completely melting. A parallelgrain boundary 75 as well as a perpendicular grain boundary 73 may beformed approximately halfway between the associated regions 74. Thesecond structure section 72 includes a crystalline structure that may beformed after the irradiation by the second beam pulse. The crystalgrained structures in this section 72 may grow radially outward from theassociated regions 74. The parallel grain boundary 75 as well as theperpendicular grain boundary 73 produced by the irradiation with thefirst pulse may remain in tact while the sample is exposed to the secondbeam pulse shaped by the second section 52 of the mask. Thus, the grainlength 76 (parallel to the direction of the crystalline structure) aswell as the grain width 77 (perpendicular to the direction of thecrystalline structure) may be controllable by the properties of the mask(e.g. pattern), rather than merely being dependent on thecharacteristics of the film. The grain width 77 formed using theembodiment of the mask according to the present invention may be widerthan the grain width 47 formed with a straight slit mask pattern, andcan be controlled using the mask pattern.

Referring to FIG. 8, a mask that may be used in an exemplary embodimentof the present invention may be divided into a first mask section 80 anda second mask section 82. Alternatively, two separate masks may be usedinstead of separate sections in one mask. The first mask section 80 maybe used to process a selected area of the thin film as an initial shot.The second mask section 82 may be used as a second shot whichimmediately follows the first shot. The first mask section 80 may havecorresponding opaque areas 84 and clear areas 85. The second masksection 82 may also have corresponding opaque areas 86 and clear areas87. While the shape of the opaque areas may be in both the first andsecond mask section may be any shape as described herein above in FIGS.2-4. The opaque areas in the first mask section 85 are preferablyprovided in rows of diamonds, circular shaped, dot shaped and/or ovalshaped areas. In one exemplary embodiment, as shown in FIG. 8, theopaque areas of both the first and second mask sections are dots.Optionally, the array of opaque areas 84 in the first mask section maybe staggered from the array of opaque areas 86 in the second masksection.

FIG. 9 depicts the resulting crystalline structure that may developusing the mask of FIG. 8. The first structure section 90 includes astructure 91 that may be produced after irradiation thereof by the firstbeam pulse. The opaque areas of the first section of the mask of FIG. 8prevent the associated regions 94 from completely melting. A parallelgrain boundary 95 as well as a perpendicular grain boundary 93 may beformed approximately halfway between the associated regions 94.crostructures. In one exemplary embodiment, the opaque areas of thesecond section 86 may be located on the edge of two islands grown fromregions produced by the first pulse. In another exemplary embodiment,the opaque areas of the second section 86 may be located on the cornerof four islands grown from opaque areas of the first region 84.

Referring next to FIG. 10, the steps executed by a computer to controlthe crystal growth process implemented with respect to FIG. 7 will bedescribed. FIG. 8 is a flow diagram illustrating the basic stepsimplemented in the system of FIG. 1. The various electronics of thesystem shown in FIG. 1 may be initialized 1000 by the computer toinitiate the process. A thin film sample, e.g., a silicon thin film, maythen be loaded onto the sample translation stage 1005. It should benoted that such loading may be either manual or robotically implementedunder the control of computer 100. Next, the sample translation stagemay be moved into an initial position 1015, which may include analignment with respect to reference features on the sample. The variousoptical components of the system may be focused 1020 if necessary. Thelaser may then be stabilized 1025 to a desired energy level andrepetition rate, as needed to fully melt the sample in accordance withthe particular processing to be carried out. If necessary, theattenuation of the laser pulses may be finely adjusted 1030.

Next, the shutter may be opened 1035 to expose the sample to a singlepulse of irradiation through a masking arrangement including at leastone of diamond shaped areas, oval shaped areas, and round shaped areas,and accordingly, to commence the sequential lateral solidificationprocess. The sample may be translated in the horizontal direction 1040.The shutter is again opened 1045 exposing previously unmelted regions toa single pulse of irradiation. The process of sample translation andirradiation 1040, 1045 may be repeated 1060 to grow the polycrystallineregion.

Next, if other regions on the sample have been designated forcrystallization, the sample is repositioned 1065, 1066 and thecrystallization process is repeated on the new region. If no furtherregions have been designated for crystallization, the laser is shut off1070, the hardware is shut down 1075, and the process is completed 1080.Of course, if processing of additional samples is desired or if thepresent invention is utilized for batch processing, steps 1005, 1010,and 1035-1065 can be repeated on each sample.

The foregoing merely illustrates the principles of the invention.Various modifications and alterations to the described embodiments willbe apparent to those skilled in the art in view of the teachings herein.It will thus be appreciated that those skilled in the art will be ableto devise numerous systems and methods which, although not explicitlyshown or described herein, embody the principles of the invention andare thus within the spirit and scope of the invention.

1. A masking arrangement for processing a thin film sample comprising: afirst section which includes at least one opaque area arranged in afirst pattern, the first section is configured to receive at least onebeam pulse thereon, and produce at least one first modified pulse whenthe at least one beam pulse is passed therethrough, the at least onefirst modified pulse including at least one first portion having apattern that corresponds to the first pattern of the first section,wherein, when the first portion is irradiated on the sample, at leastone first region of the sample is prevented from being completely meltedthroughout its thickness; and a second section associated with the firstsection, the second section including a further area arranged in asecond pattern, the second section being configured to receive at leastone further beam pulse thereon, and produce at least one second modifiedpulse when the at least one further beam pulse is passed therethrough,the at least one second modified pulse including at least one secondportion having a pattern that corresponds to the second pattern of thesecond section, wherein, when the second portion is irradiated on thesample, at least one second region of the sample irradiated by thesecond portion is completely melted throughout its thickness, whereinwhen the first region is irradiated by the at least one second modifiedpulse, the second portion of the at least one second modified pulsecompletely melts the at least one first region throughout its thickness.2. The masking arrangement as in claim 1, wherein at least one of thefirst pattern and the second pattern comprises at least one of diamondareas, oval areas, dot areas and round areas.
 3. The masking arrangementas in claim 1, wherein, the first pattern extends approximately along afirst horizontal axis, the first pattern having a width measured alongthe vertical axis, a second area of the second section extendsapproximately along the first horizontal axis, the second section beingconfigured to permit the at least one first region to be completelymelted throughout its thickness by the second modified pulse, the secondarea being offset horizontally from the first pattern, the second areahaving a width measured in the vertical axis that is at least equal tothe width of the first pattern, and the second pattern extendsapproximately along a second horizontal axis and vertically offset fromthe first horizontal axis, wherein the second pattern is configured toprevent at least one third region of the sample from being completelymelted throughout its thickness.
 4. A masking arrangement as in claim 3,wherein the first section includes at least one further opaque areaarranged in a third pattern extending approximately along a thirdhorizontal axis, wherein the third horizontal axis is vertically offsetfrom the first horizontal axis, wherein the third pattern issubstantially aligned vertically with the first pattern, wherein thethird pattern is configured to prevent at least one fourth region of thesample from being completely melted throughout its thickness, wherein aposition of the third horizontal axis is such that the second horizontalaxis is between the first horizontal axis and the third horizontal axis.5. The masking arrangement as in claim 4, wherein the third patterncomprises at least one of diamond areas, oval areas, dot areas and roundareas.
 6. The masking arrangement of claim 3, wherein the secondhorizontal axis extends approximately along a centerline in between thefirst and third horizontal axes.
 7. The masking arrangement of claim 4,wherein, elements of the first pattern are approximately equidistantfrom other elements of the first pattern, and elements of the thirdpattern are approximately equidistant from other elements of the thirdpattern.
 8. The mask arrangement of claim 1, wherein the second patterncomprises one or more substantially parallel lines.
 9. A method forprocessing a thin film sample, comprising the steps of: providing atleast one beam on a first section of a masking arrangement to produce atleast one first modified pulse when the at least one beam is passedtherethrough, the first section which includes at least one opaque areaarranged in a first pattern, the at least one first modified pulseincluding at least one first portion having a pattern that correspondsto the first pattern, wherein, when the first portion is irradiated onthe sample, at least one first region of the sample is prevented frombeing completely melted throughout its thickness; based on thedimensions of the masking arrangement, translating at least one of thethin film sample and the beam relative to the other one of the thin filmsample and the beam; and providing at least one further beam on a secondsection of a masking arrangement to produce at least one second modifiedpulse when the at least one further beam is passed therethrough, thesecond section associated with the first section, the second sectionincluding a further area arranged in a second pattern, the at least onesecond modified pulse including at least one second portion having apattern that corresponds to the second pattern, wherein, when the secondportion is irradiated on the sample, at least one second region of thesample irradiated by the second portion is completely melted throughoutits thickness; wherein, when the first region is irradiated by the atleast one second modified pulse, the second portion of the at least onesecond modified pulse completely melts the at least one first regionthroughout its thickness.
 10. The method of claim 9, wherein at leastone of the first pattern and the second pattern comprises at least oneof diamond areas, oval areas, dot areas and round areas.
 11. The methodof claim 9, wherein, the first pattern extends approximately along afirst horizontal axis, the first pattern having a width measured alongthe vertical axis, a second area of the second section extendsapproximately along the first horizontal axis, the second section beingconfigured to permit the at least one first region to be completelymelted throughout its thickness by the at least one second modifiedpulse, the second area being offset horizontally from the first pattern,the second area having a width measured in the vertical axis that is atleast equal to the width of the first pattern, and the second patternextends approximately along a second horizontal axis and verticallyoffset from the first horizontal axis, wherein the second pattern isconfigured to prevent at least one third region of the sample from beingcompletely melted throughout its thickness.
 12. The method of claim 11,wherein the first section includes at least one further opaque area in athird pattern extending approximately along a third horizontal axis,wherein the third horizontal axis is vertically offset from the firsthorizontal axis, wherein the third pattern is substantially alignedvertically with the first pattern, wherein the third pattern isconfigured to prevent at least one fourth region of the sample frombeing completely melted throughout its thickness, wherein a position ofthe third horizontal axis is such that the second horizontal axis isbetween the first horizontal axis and the third horizontal axis.
 13. Themethod of claim 12, wherein the third pattern comprises at least one ofdiamond areas, oval areas, dot areas and round areas.
 14. The method ofclaim 11, wherein the second horizontal axis is approximately along acenterline in between the first and third horizontal axes.
 15. Themethod of claim 12, wherein, elements of the first pattern areapproximately equidistant from other elements of the first pattern, andelements of the third pattern are approximately equidistant from otherelements of the third pattern.
 16. The method of claim 9, wherein thesecond pattern comprises one or more substantially parallel lines.
 17. Asystem for processing a thin film sample, comprising: a mask, aprocessor to activate a device to irradiate through the mask, theprocessor being configured to perform the steps of: providing at leastone beam on a first section of a masking arrangement to produce at leastone first modified pulse when the at least one beam is passedtherethrough, the first section which includes at least one opaque areaarranged in a first pattern, the at least one first modified pulseincluding at least one first portion having a pattern that correspondsto the first pattern, wherein, when the first portion is irradiated onthe sample, at least one first region of the sample is prevented frombeing completely melted throughout its thickness, based on thedimensions of the masking arrangement, translating at least one of thethin film sample and the beam relative to the other one of the thin filmsample and the beam, and providing at least one further beam on a secondsection of a masking arrangement to produce at least one second modifiedpulse when the at least one further beam is passed therethrough, thesecond section associated with the first section, the second sectionincluding a further area arranged in a second pattern, the at least onesecond modified pulse including at least one second portion having apattern that corresponds to the second pattern, wherein, when the secondportion is irradiated on the sample, at least one second region of thesample irradiated by the second portion is completely melted throughoutits thickness; wherein, when the first region is irradiated by the atleast one second modified pulse, the second portion of the at least onesecond modified pulse completely melts the at least one first regionthroughout its thickness.
 18. The system of claim 17, wherein at leastone of the first pattern and the second pattern comprises at least oneof diamond areas, oval areas, dot areas and round areas.
 19. The systemof claim 17, wherein, the first pattern extends approximately along afirst horizontal axis, the first pattern having a width measured alongthe vertical axis, a second area of the second section extendsapproximately along the first horizontal axis, the second section beingconfigured to permit the at least one first region to be completelymelted throughout its thickness by the at least one second modifiedpulse, the second area being offset horizontally from the first pattern,the second area having a width measured in the vertical axis that is atleast equal to the width of the first pattern, and the second patternextends approximately along a second horizontal axis and verticallyoffset from the first horizontal axis, wherein the second pattern isconfigured to prevent at least one third region of the sample from beingcompletely melted throughout its thickness.
 20. The system of claim 19,wherein the first section includes at least one further opaque areaextending in a third pattern approximately along a third horizontalaxis, wherein the third horizontal axis is vertically offset from thefirst horizontal axis, wherein the third pattern is substantiallyaligned vertically with the first pattern, wherein the third pattern isconfigured to prevent at least one fourth region of the sample frombeing completely melted throughout its thickness, wherein a position ofthe third horizontal axis is such that the second horizontal axis isbetween the first horizontal axis and the third horizontal axis.
 21. Thesystem of claim 20, wherein the third pattern comprises at least one ofdiamond areas, oval areas, dot areas and round areas.
 22. The system ofclaim 20, wherein the second horizontal axis is approximately along acenterline in between the first and third horizontal axes.
 23. Thesystem of claim 22, wherein, elements of the first pattern areapproximately equidistant from other elements of the first pattern, andelements of the third pattern are approximately equidistant from otherelements of the third pattern.
 24. The system of claim 19, wherein thesecond pattern comprises one or more substantially parallel lines.